Abstract
We characterized cyclic electron flow around PSI (CEF-PSI) using the intact leaves of rice which PSII was photoinhibited, to elucidate the effect of photosynthetic linear electron flow (LEF), estimated from QY(PSII), on CEF-PSI. Rice leaves were exposed to high intensity of light under photosynthesis-limited conditions. With the light treatments, maximum quantum yield of PSII and net photosynthesis rate decreased. NPQ of Chl fluorescence was suppressed by the light treatments. On the other hand, qL, the Chl fluorescence parameter for the redox level of PQ, increased. The ratio of P700+ to total P700 also increased. These results indicate that photoinhibition of PSII induced the increase in oxidation of photosynthesis electron transport system, especially PQ. Different from LEF activity, the relative electron flux in PSI was not affected by PSII photoinhibition. Furthrmore, the relationship between QY(PSI) and QY(PSII) with the slope below 1 was kept even after the photoinhibition. However, the activity of CEF-PSI increased, because LEF activity decreased. The molecular mechanism for the regulation of CEF-PSI activity and its physiological significance will be discussed.
